The DUP has hit out at a "scurrilous attempt" to blame Arlene Foster for the botched energy scheme that could cost taxpayers £400 million.

It disputed claims the First Minister failed to follow up on whistleblower concerns about the Renewable Heat Incentive, releasing an email at the centre of the deepening controversy.

Thousands signed up to the RHI - a deluge that ultimately forced its closure, but not before Stormont had been left with a huge bill.

Yesterday in a day of further dramatic developments:

- The SDLP said it would table a no confidence motion against Mrs Foster, and called on Sinn Fein to support it.

- It emerged MLAs would be brought back from their Christmas break next week to discuss the crisis.

- The UUP said the UK Government could no longer ignore the "national scandal".

Mrs Foster has faced intense public scrutiny over her role in the RHI when she was Enterprise Minister.

She has rejected calls for her resignation over her handling of the error-ridden scheme.

The controversy has deepened over claims a whistleblower flagged concerns about abuse of the scheme two years before it was shut down.

They raised issues with Mrs Foster, the then Minister of Enterprise, Trade and Investment.

But last night the DUP released what it said was a copy of the 2013 email, pointing out that it raised no specific concerns about RHI. The party said it simply asked for a meeting on energy efficiency matters.

The DUP said that was the only email that Ms Foster received from the individual whistleblower and said she referred it to her officials at the time.

DUP deputy leader Nigel Dodds said: "There has been a quite scurrilous attempt to blame Arlene Foster for the RHI saga. The endlessly repeated claim has been that she failed to follow up on the whistleblower concerns. Now we know that no such concerns were raised with her."

Mr Dodds accused Opposition parties and some sections of the media of engaging in a "disgraceful and baseless blame game", and called for an apology.

But the UUP said it would make no apology after raising the issue in Parliament yesterday. South Antrim MP Danny Kinahan said: "This is taxpayers' money literally going up in smoke." He added: "I hope the UK Government will keep a close eye on proceedings.

"This is a national scandal and Westminster should understand its full extent."

Yesterday it emerged Mrs Foster would address a special sitting of the Assembly on Monday over the RHI. The Executive put off any decisions on how the projected £400m spend can be reduced until early in the new year - when a new public consultation will also be launched.

Proposals for dealing with the fallout from the scheme were not on the agenda for the final Executive meeting before Christmas.

The controversy escalated last night when the SDLP said it planned to table its motion. Colum Eastwood said Sinn Fein had a choice to "stand with us and with the public who are demanding the highest standard of accountability, or they can continue to stand in the shadow of the DUP, propping up a First Minister who treats accountability with disdain".

He added: "If Mrs Foster will not stand aside, then the Assembly must act to remove her from office and fully scrutinise this scandal. She has lost all credibility and anything less will further erode faith in our institutions."

However, Sinn Fein said it will not back the SDLP motion.

Newry and Armagh MLA Conor Murphy said: "The motion is premature and does not address any of the core issues. The reason for the Assembly meeting on Monday is to allow Members and the public to hear what the First Minister has to say on a matter of grave public concern.

"We also need disclosure of all information and we need to know who benefited from this scheme and why it wasn't brought to a close much earlier."

Meanwhile, an interim report into the scheme by consultants PWC, revealed on the Nolan Show, reportedly concluded that less than half of the total installations inspected (47%) under the scheme were generating heat for an eligible purpose.